1. Field of the Invention
The present invention relates to an optical recording method of and an optical recording apparatus for use in recording data, for example, in a digital video disk (DVD) using a light beam.
2. Description of the Related Art
With the development of multimedia pointing to a high information-oriented society, a still higher performance and a still greater capacity of the optical disk are demanded. Seeing from the function and the purpose, the optical disk is roughly classified into three kinds, namely, the optical disk for read only operation in which information data recorded during the disk-cutting are only reproduced, the optical disk for write once operation in which data can be recorded once but the data cannot be rewritten, and the rewritable optical disk in which data can be rewritten repeatedly.
Of these disks, in particular, for the rewritable optical disk in which information data can be rewritten, greater capacity is demanded and so, using only a groove recording method in which information data are recorded only on a groove portion which comprises a spiral groove formed on the optical disk surface, it is impossible to satisfy the needed recording capacity. Thus, in the rewritable optical disk, a land-groove recording method in which information data are recorded on the groove portion as well as a portion called the land portion between the groove portions has been adopted.
In an optical disk recording/reproducing apparatus, in order to record information data on a target track of the optical disk, an optical pickup must be moved onto a target track of the optical disk and then the laser beam must be irradiated onto the target track. To this end, it is necessary to position the optical pickup to the target location. As a servo system which moves the optical pickup to the target location in the radial direction of the optical disk, there is a tracking servo system.
The tracking servo system is comprised of a tracking coil of an actuator system in the optical pickup and a tracking servo circuit. The actuator system makes the optical pickup to perform fine tracking operation, for example, by a two axes actuator.
When the laser beam chases the track for tracking to read an address and a difference from a target address is known, a fine seeking by that difference is performed. At this time, if an eccentric velocity is large, it is difficult to perform a stable seeking control. Accordingly, after waiting until the eccentric velocity becomes small, it finally reaches the target track and then performs a recording operation by the land-groove recording method in which information data are recorded on the groove portion as well as the land portion between the groove portions of the optical disk.
However, as the rewritable optical disk is made to have a large capacity, it is required that a track pitch is constructed as narrow as possible. Consequently, a diameter of the laser beam of the optical pickup has come to cover not only the groove portion which is the target for positioning the track but also the already recorded land portion adjacent to the side of the internal circumference of the disk and a non-recorded land portion on the side of the external circumference of the disk.
As a result, when information data is recorded on the groove portion, a cross-erasing is caused, in which information data of the already recorded land portion adjacent to the groove portion that is the target for positioning, on the side of the external circumference of the disk are erased.
FIG. 1 shows a specific operation according to a conventional land-groove recording method.
Referring to FIG. 1, toward the external circumference side of the disk are arranged a land L1, a groove G1, a land L2 and a groove G2. The recording operation will proceed in the direction from the land L1 to the groove G1, the land L2 and the groove G2.
Referring to FIG. 1, record marks 130 and 131 are formed first on the land L1 on the side of the internal circumference of the disk in the direction of rotation of the disk by the laser beam. Next, new record marks 132 and 133 are formed on the groove G1 adjacent to the side of the external circumference of the land L1 by the laser beam overwriting. At this time, while the record marks 130 and 131 are formed on the land L1 before the overwriting operation, the diameter of a laser beam spot 134 is larger than a track width d being each width of the land L1 and the groove G1, and besides, the laser spot is made to track a center of the width of each of the land L1 and the groove G1, so that they are recorded beyond the groove G1 sticking out into the internal circumference side and the external circumference side of the disk. In this condition, the new record marks 132 and 133 are formed on the groove G1 after the overwriting operation on the groove G1.
Firstly, as shown in the groove G1, the new record mark 132 is formed on the groove G1 after overwriting. At this time, as shown in the groove G1, there exists the record mark 130 formed by the laser beam on the land L1 and the groove G1 before the overwriting operation. In this case, by forming the new record mark 132 on the groove G1, the laser beam overwrites a portion of the record mark 130, which is indicated by a broken line, sticking out into the land L1 and cross-erases a remaining portion of the record mark 130, which is indicated by the broken line in the record mark 130, sticking out into the land L1. In this way, by forming the new record mark 132, on the groove G1 the record mark 130 in the land L1 is overwritten and at the same time cross-erased. Therefore, the record mark 130 is not formed in the full track width d of the land L1, but formed in an effective record width b narrowed by an erase width c.
Likewise, as shown subsequently in the direction of rotation of the disk in the groove G1, the new record mark 133 is formed on the groove G1 after the overwriting. At this time, as shown in the groove G1 there exists the record mark 131 formed by the laser beam on the land L1 and the groove G1 before the overwriting operation. Here, by forming the new record mark 133 on the groove G1, a portion of the record mark 131, in the land L which is indicated by the broken line, is overwritten by the laser beam sticking out into the land L1, and a remaining portion of the record mark 131, which is indicated by the broken line in that mark 131 is cross-erased by the laser beam sticking out into the land L1. In this manner, by forming the new record mark 133 on the groove G1, the record mark 131 on the land L1 is overwritten as well as cross-erased. Therefore, the record mark 131 is not formed in the full track width d of the land L1, but formed in an effective record width b narrowed by an erase width c.
Likewise, as shown in the land L2, a new record mark 135 is formed on the land L2 after the overwriting. At this time, as shown in the land L2 there exists the record mark 132 formed by the laser beam on the groove G1 and land L2 before the overwriting operation. Here, by forming the new record mark 135 in the land L2, a portion of the record mark 132, which is indicated by the broken line is cross-erased by the laser beam sticking out into the land L2, and a remaining portion of the record mark 133, which is indicated by the broken line in the groove G1, is cross-erased by the laser beam sticking out into the land L2. Further, by forming a new record mark 136 in the land L2, a portion of subsequent record mark 133, which is indicated by the broken line in the groove G1, is overwritten by the laser beam sticking out into the land L2.
In this manner, by forming the new record mark 135 in the land L2, the record marks 132, 133 on the groove G1 are cross-erased and by forming the new record mark 136 in the land L2, the record mark 133 on the groove G1 is overwritten. Therefore, the record marks 132 and 133 are not formed in the full track width d of the groove G1, but formed in an effective record width b narrowed by the erase width c.
FIG. 2 shows a recorded state of the record mark by the conventional land-groove recording method. As is shown in FIG. 2, when a record mark 140 is formed on the land L1, the record mark 140 is formed sticking out into the adjacent groove G1 in the external circumference side of the disk. Moreover, when a new record mark is formed on the groove G1, a portion of the record mark 140, which is indicated by the broken line, already recorded on the land L1 will be overwritten or cross-erased.
Essentially, if information data are recorded by forming the record marks in the proper area of the groove portion and the land portion, namely in the full track width d in the track width direction, it would be possible to improve the S/N ratio by reproducing all the recorded data as reproduced data during reproduction.
However, if the cross-erasing of information data in adjacent tracks is caused in this manner, it is impossible to reproduce all the recorded data during reproduction. Accordingly, a level of reproduced signals is lowered or a noise is introduced into the reproduced data. Under the worst conditions, it may sometimes be impossible to obtain any reproduced data.
In this way, with the conventional optical recording method cross-erasing has been caused, in which information data recorded on the land portion adjacent to the groove portion to be recorded are erroneously erased. However, since no counter measure against the cross-erasing has been considered, there exists a disadvantage in which not all of the recorded data are kept in the recorded state or noise is introduced into the reproduced data or no reproduced data can be obtained.
In particular, with a land-groove recording and reproducing method which is expected as a recording method enabling a high density recording, if the width of the land portion and the groove portion in the track direction is made narrower than a diameter of the laser spot, then cross-erasing becomes a serious problem when recording data.